Assimilation-oriented Dual-polarization Radar Inversion Of Raindrop Spectrum To Simulate Precipitation

Microphysical properties of raindrops such as scale,axial ratio,shape,velocity,and size distribution are important parameters reflecting the physical nature of rainfall.In recent years,with the widespread application of meso-scale numerical models in meteorological operations and increasing number of meteorological radar systems,it has been becoming the main way to develop and improve to improve the accuracy of quantitative precipitation forecasting using radar data for assimilation.Polarimetric radars can only detect the backscattering signal of raindrop particles and cannot directly detect the raindrop size distribution(DSDs)information.Although a ground two-dimensional video disdrometer(2DVD)can obtain the DSDs information,but it cannot describe the spatiotemporal characteristics of raindrop size in convection.Therefore,the combination of the 2DVD and polarimetric radar which can be used to obtain DSDs information over a larger area and with higher spatiotemporal resolutions.Affected by geography and other factors,the raindrop spectrum characteristics of the rainfall system in each region of China are significantly different from other countries and regions.Therefore,establishing a precipitation parameter retrieval operator which is suitable for the raindrop spectrum characteristics of the weather system in our country and region is needed.This is the prerequisite for radar quantitative precipitation estimation(QPE)and the basis of radar data assimilation in numerical prediction.Based on the above reasons,this paper integrates the retrieval methods of raindrop spectrum at home and abroad,and establishes a scheme of retrieval raindrop spectrum for polarimetric radar in South China monsoon region.For the first time,the C-band polarimetric radar has been used for the related research and application of the spectral characteristics of precipitation in southern China.Firstly,in order to obtain more high-quality products from the polarimetric radar,the quality control is required,which lays the foundation for the assimilation of radar data.A quality analysis of the Guangzhou S-band polarimetric radar data is performed to obtain the effective threshold of radar data.The quality control of Xinfeng C-band polarimetric radar is carried out to obtain accurate radar data.Then a simulator for calculating the reflectivity(Z_H)and the differential reflectivity(Z_DR)of the polarimetric radar by the parameters such as the precipitation particle number concentration and particle axis ratio is constructed.Furthermore,the effects of different axial ratios and wavelengths on the polarimetric radar simulation are analyzed.Finally,the shape-slope(?-?)relationship of this region is statistically analyzed using the raindrop sample observations from 2DVD.Simulated data of polarimetric radar Z_H and Z_DR are combined with DSD fitting to determine the Z_DR-?and log₁₀(Z_H/N₀)-?relationships.The relationship between the N₀,?,?and polarimetric radar parameters is presented,and a scheme using polarimetric radar to retrieve the DSDs is developed to realize their complementarity in the observation space.In this research,two different precipitation events are used to test the DSDs retrieval scheme.The C-band polarimetric radar located in Xinfeng,the 2DVD at Xinfeng Station,and the Z_H and Z_DR data obtained from the scattering simulation are used.The?,?,N₀ and N(D)are obtained by the retrieval scheme,and the precipitation characteristics of rainfall intensity(R),mass-weighted mean diameter(D_m)and intercept parameter(N_w)are obtained.The observation data from the 2DVD at Xinfeng Station are used to verify the radar retrieval results.The results show that the method using the C-band polarimetric radar retrieve the DSDs based on the gamma size distribution which is developed in South China for the first time is highly reliable.This method is not only capable of testing the prediction of the model data assimilation system and determining the error sources,but can also improve the microphysical precipitation processes analysis and radar QPE.This estimation scheme lays the foundation for the assimilation of radar data.